1. Field of the Invention:
The present invention relates to power supplies. More specifically, the present invention relates to power conditioners for use in power supplies.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art:
Power supply circuits typically include a rectifier circuit which converts an input alternating current (AC) input waveform to a direct current (DC) waveform. These rectifiers often pull harmonic currents from the source along with the desired fundamental signal. The harmonics impede the efficiency of power conversion and induce noise in load circuits.
For example, high power 3 phase AC to DC converters typically use off-line rectifies. Diodes or silicon controlled rectifiers (SCRs) control the rectification process by controlling the ON time of the rectifier. The output is smoothed or filtered by a large capacitor which provides a low ripple DC bus voltage for power distribution, motor control, lighting and etc. The circuit pulls harmonic currents which do not convert to work and are considered lost energy. The quality factor of the harmonic content is the "power factor". The power factor of typical high power rectifiers is 0.6 to 0.7. This translates to 30-40% usable power lost in the rectification process.
U. S. Pat. No. 4,680,689, issued Jul. 14, 1987, to Payne et. al. describes a three-phase AC to DC power converter which employs a separate DC to DC converter on each phase connected in parallel to reduce harmonic currents. Unfortunately, the DC to DC converters share the DC load current without regulation. Therefore, for example, if the load was one third the maximum level, the output impedance of each DC to DC converter would have to be exactly matched to provide equal sharing. Since there cannot be an exact match because of device and manufacturing tolerances, the lowest source impedance would dominate the DC load and cause an unbalanced load at the power source. In a four wire system, the imbalance would be in the neutral wire which could cause a safety hazard by overloading the neutral wire causing excessive voltage drop or difference between adjacent equipment.
Thus, there is a need in the art for a technique for converting alternating current to direct current at all power levels with a high power factor and minimal harmonic currents.